The present invention relates to a method for the manufacture of resistive wire touch screens on flat-panel displays with a common substrate.
Electronic devices typically include a computing engine, a display and an interactive device responsive to the input of a user. For example, a computer may include a computing circuit, a CRT for display, and a keyboard and mouse responsive to a user""s input. As a second example, a Personal Digital Assistant includes a computing circuit, an LCD display, and a touch screen formed over the LCD display, together with some buttons. Many electronic devices, in particular mobile devices, miniature devices, devices that require a reprogrammable interface, or devices that require a robust and simple user interaction mechanism, rely upon touch screens placed over a display to provide user interaction capabilities to the device.
There are many touch screen technologies such as resistive wire, acoustic, and infra-red. These are generally placed above either a CRT screen or LCD screen to provide the required interactive functionality in a single component composed of two parts. Typically, the display (for example, LCD or CRT) is manufactured while the touch screen is made separately. After the display and touch screen are manufactured, they are integrated in a common housing to provide a single component that can be built into a complete electronic device.
Resistive wire touch screens are built upon a substrate that has coated upon it a resistive film, typically indium tin oxide (ITO) at a specified thickness, uniformity and resistivity. Resistive touch screen materials, such as spacers, conductive films, etc. are carefully formed upon the coated substrate to create a resistive touch screen. When combined with a display, the multi-layer component has inferior optical characteristics to the display device alone due to inter-layer reflections, has redundant manufacturing steps, and redundant components. Moreover, the additional step of integrating the components raises manufacturing costs for the complete device. The manufacturing processes for display-and-touch-screen devices are well known in the art and products are available today from a variety of vendors. For example, U.S. Pat. No. 5,795,430 issued Aug. 18, 1998 to Beeteson et al., describes an adhesive material dispensed onto a faceplate and used to attach a touch screen.
A new class of display devices based upon organic light-emitting diodes (OLEDs) is formed by depositing patterned conductive and organic materials upon a substrate. This substrate can be identical to the substrate used for resistive wire touch screens. Moreover, some of the materials used for the patterned conductive materials are similar to, or the same as, those used for the resistive films, but their uniformity, thickness and resistivity may vary. Passive matrix OLED displays are made by patterning a conductive material that is formed on a substrate. Active matrix OLED displays are typically made by patterning a conductive material on semiconducting materials comprising thin film transistor (TFT) circuitry. The TFTs are formed on a substrate. For an OLED display, the conductive material is ideally a low resistivity film, whereas for a touch screen a controlled higher resistivity film is employed. Once the conductive pattern is formed, organic materials are deposited, followed by any remaining conductive elements, planarization layers and other layers as known in the prior art. Connecting pads are defined as part of the conducting pattern and are wire-bonded to a cable after the device is encapsulated. The process by which the OLED display device is made uses well-known photo-lithographic, deposition, bonding, and encapsulation methods common-place in the integrated circuit industry. However, a problem exists with the conventional practice of forming separate OLED displays and touch screens and then combining them with a conventional mount, in that the additional layers in the touch screen reduce the brightness of the display, reduces the optical quality of the display due to additional internal reflections from the layers of the touch screen, and add cost due to the need for two substrates and a complex housing for the two elements.
There is a need therefore for an improved method for manufacturing an integrated resistive touch screen and OLED display that reduces redundant components in the devices, reduces cost, improves optical qualities, and is more robust.
The need is met according to the present invention by providing a method of manufacturing a display device having two components, an OLED display formed on a film on one side of a substrate and a touch screen formed on a film on the other side of the substrate, the OLED display including components that are sensitive to high temperatures, that includes the steps of; partially forming one of the components on one side of the substrate; applying a protector over the partially constructed component; forming the other component of the display device on the other side of the substrate; removing the protector, and completing the formation of the one component on the one side of the substrate.
The present invention has the advantage that it reduces the number of components required to build an integrated OLED display and resistive touch screen device, reduces the number of manufacturing steps, reduces the manufacturing costs, reduces the combined size of the display and touch screen device, and provides superior optical performance.